Fostex DP8

Paul White tries a simple but useful digital switching system that can be used with S/PDIF or ADAT‑format signals.

As more items of studio equipment become digital, the problem of patching them together grows increasingly complicated, because, as with analogue gear, you occasionally need to change your setup to perform specific tasks. In the analogue domain the job is generally done with mechanical patchbays, but there's no direct digital equivalent. There are some programmable digital patchbays around, but these can be expensive and difficult to operate, especially when you only want to make a simple patching change. Life is also complicated further by the fact that there are several types of digital connection format, predominantly ADAT optical, AES/EBU XLR and S/PDIF on both phono and optical ports.

Fostex have come up with one solution to the problem, in the shape of the DP8, a non‑programmable 8‑in, 8‑out digital routing box where the routing is controlled entirely by rotary switches. Both phono and optical inputs and outputs are provided, but there's no XLR option.

The secret of the DP8 is simplicity — there's no data conversion or other clever processing inside. The most complicated thing that happens is that phono ins are converted to optical, and vice versa. If you feed in an ADAT signal, you'll get an ADAT signal out, and if you feed in S/PDIF from a DAT machine or similar source, then S/PDIF is what you'll get out. You can't merge data streams (that would require a digital mixer), though it is quite possible to split one input to feed several destinations.

The Hardware

The DP8 is presented as a shallow 1U rackmount device (wall‑wart powered, of course), with two phono ins and outs (channels 1 and 2) and six optical ins and outs (channels 3 to 8). Inputs 7 and 8 are located on the front panel for convenient access when patching in visiting gear, whereas all the others are on the back panel for permanent connection. The brief manual states that dust caps are fitted to all optical ins and outs, and that these should be replaced when the optical ports are not in use, but the review sample came without dust caps.

The only user controls are eight rotary switches, each of which relates to one of the eight outputs. Turning a switch selects which of the eight inputs is routed to that output; there's no 'off' position, so one of the eight inputs is always selected. There are no restrictions on which signals are routed to which outputs, but clearly there's no sense in routing an ADAT optical input to a phono output, as the data stream will still be in ADAT format and thus will be unreadable by an S/PDIF phono input. However, optical S/PDIF can be sent to a co‑axial phono S/PDIF output with no problem.

The simplest way to connect equipment to the DP8 is probably to use I/O 1 for one machine, I/O 2 for another machine and so on, though you don't have to work in this way if you don't want to. There's room above the selector knobs to fix a strip of tape carrying the names of the connected devices, but there's no official scribble strip. Furthermore, because the DP8 doesn't have a programming system it might be useful to write down the knob settings for your most common patches, so that you don't have to figure out everything from first principles every time.

The secret of the DP8 is simplicity — there's no data conversion or other clever processing inside.

Is It Useful?

The DP8 is such a simple device that I hardly need to talk about how it performs in use (suffice it to say that signals go where they're supposed to go), but I think a few suggestions on where it might come in handy are in order. In a studio where there are, for example, two DAT machines and a computer with a digital interface, the DP8 could swap between a configuration where one DAT machine is connected ready for cloning tapes onto the other machine, and a completely different setup where one DAT machine might be used as the A‑D converter feeding the digital card and the other monitoring the card's output. Similar situations could occur with ADATs, digital mixers and ADAT‑compatible soundcards, where sometimes your ADATs will need to be connected to each other for track copying and cloning, while at other times you'll want to connect your ADATs to your soundcard or mixer. I know, in my own digital editing setup, that there are times when I'd like to be able to change my digital connections more easily, and with a device such as the DP8 I could feed the output from my editing system into both DAT machines at the same time, to simplify patching when making two simultaneous DAT copies from disk.

To me, the greatest limitation of this device is the fact that the I/O ports are mainly optical, while most studio DAT machines have co‑axial phono S/PDIF connectors. Of course, if you're using mainly ADATs this is an advantage. If all the outputs had been available on both optical and phono simultaneously (as was the case for the programmable Midiman Digipatch unit we looked at in the December 1997 issue of SOS), the connectivity options would have been rather more flexible. Incidentally, the manual warns against using two or more DP8s in cascade, because of the risk of introducing clock jitter. Other than that, the unit is simple in concept and does just what it says on the tin!

Summary

This box is ideal for anyone who has a fairly simple digital setup and who needs to switch between relatively few configurations. The ratio of optical to co‑axial connectors makes the DP8 most useful for those who have equipment with mainly optical interfaces, and because the optical connectors can also handle ADAT information, there are numerous applications in ADAT‑based studios (or systems using the ADAT protocol).

This isn't a unit that needs the hard sell — you either have an application for it or you don't, and if you do you'll be choosing between the DP8 and something programmable and more flexible, that's probably a lot more expensive.